1. Field of the Invention
The present invention relates to an organic electroluminescence display device and a method of manufacturing an organic electroluminescence display device, and more particularly, to an organic electroluminescence display device in which a gate electrode of a driving transistor and an electrode of an organic electroluminescence device are patterned simultaneously, thereby reducing the number of masks used in the manufacturing process.
2. Discussion of the Background
Generally, electroluminescence display devices are self-emitting displays in which fluorescent organic compounds are electrically excited to emit light. These display devices may be operated at low voltages, may be formed with thin films, and have wide viewing-angles and rapid response. Therefore, they are regarded as next-generation displays to replace liquid display devices.
Electroluminescence display devices may be inorganic or organic devices according to whether a light-emitting layer comprises an inorganic or organic material.
An organic electroluminescence display device includes an organic film, which may be formed in a predetermined pattern between electrode layers on a transparent insulating substrate, such as glass.
In the organic electroluminescence display device, applying a voltage to an anode electrode causes holes to migrate from the anode to a light emitting layer via a hole transport layer, and applying a voltage to a cathode electrode causes electrons to migrate from the cathode to the light emitting layer via an electron transport layer. The electrons and the holes recombine in the light emitting layer to create excitons, and when the excitons transition from an excited to a ground state, fluorescent molecules of the light emitting layer emit light, thereby forming images.
Active matrix (AM) organic electroluminescence display devices include at least two thin film transistors (TFTs) per pixel. One TFT may be used as a switching device that controls the pixel's operation, and the other may be used as a driving device that drives the pixel.
A TFT includes a semiconductor layer having drain and source regions, which may be doped with highly-concentrated impurities, and having a channel area formed between the drain and source regions, a gate insulator formed on the semiconductor layer, a gate electrode formed on the gate insulator above the channel area, and drain and source electrodes connected to the drain and source regions, respectively, via a contact hole. An interlayer insulator is interposed between the drain and source electrodes and the gate electrode.
FIG. 1 shows an effective display area 110 and a non-effective display area 120 of an organic electroluminescence display device 100. FIG. 2 is a circuit diagram of an image displaying transistor unit 300, which is formed in the effective display area 110, and a driving signal controlling transistor unit 200, which is formed in the non-effective display area 120.
The driving signal controlling transistor unit 200 may include a combination of various transistor logics, and it transmits a driving signal via a scan line to toggle a switching transistor TFTsw 310 of the image displaying transistor unit 300.
The image displaying transistor unit 300 may include at least one switching transistor TFTsw 310, at least one driving transistor TFTdr 320, and a rechargeable capacitor Cst. The switching transistor TFTsw 310 is driven by a scanning signal Scan, and it transmits a data signal Data applied to a data line. The driving transistor TFTdr determines the amount of current flowing into an organic electroluminescence device OLED via a driving line Vdd according to the data signal transmitted through the switching transistor TFTsw, that is, according to the voltage difference (Vgs) between a gate and a source. The rechargeable capacitor Cst stores the data signal that is transmitted through the switching transistor TFTsw during one frame.
A conventional method of manufacturing such an organic electroluminescence display device requires as many as 10 masks. The use of so many masks may prolong and complicate the manufacturing process, thereby resulting in higher manufacturing costs.